Evidence for azimuthal variations of the oxygen-abundance gradient tracing the spiral structure of the galaxy HCG 91c ^⋆

¹ European Southern Observatory, Av. Alonso de Córdova 3107, 763 0355 Vitacura, Santiago, Chile
e-mail: frederic.vogt@alumni.anu.edu.au
² Instituto de Astrofísica de Andalucía, CSIC, Apdo. Correos 3004, 18080 Granada, Spain
³ Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australia
⁴ Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA

Received: 3 October 2016
Accepted: 23 December 2016

Abstract

Context. The distribution of elements in galaxies forms an important diagnostic tool to characterize these systems’ formation and evolution. This tool is, however, complex to use in practice, as galaxies are subject to a range of simultaneous physical processes active from pc to kpc scales. This renders observations of the full optical extent of galaxies down to sub-kpc scales essential.

Aims. Using the WiFeS integral field spectrograph, we previously detected abrupt and localized variations in the gas-phase oxygen abundance of the spiral galaxy HCG 91c. Here, we follow-up on these observations to map HCG 91c’s disk out to ~2 R_e at a resolution of 600 pc, and characterize the non-radial variations of the gas-phase oxygen abundance in the system.

Methods. We obtained deep MUSE observations of the target under ~0.6 arcsec seeing conditions. We perform both a spaxel-based and aperture-based analysis of the data to map the spatial variations of 12 +log (O/H) across the disk of the galaxy.

Results. We confirm the presence of rapid variations of the oxygen abundance across the entire extent of the galaxy previously detected with WiFeS, for all azimuths and radii. The variations can be separated in two categories: a) localized and associated with individual H ii regions; and b) extended over kpc scales, and occurring at the boundaries of the spiral structures in the galaxy.

Conclusions. Our MUSE observations suggest that the enrichment of the interstellar medium in HGC 91c has proceeded preferentially along spiral structures, and less efficiently across them. Our dataset highlights the importance of distinguishing individual star-forming regions down to scales of a few 100 pc when using integral field spectrographs to spatially resolve the distribution of oxygen abundances in a given system, and accurately characterize azimuthal variations and intrinsic scatter.